A three-dimensional statistical reconstruction model of grapevine (Vitis vinifera) simulating canopy structure variability within and between cultivar/training system pairs

Background and Aims

In grapevine, canopy-structure-related variations in light interception and distribution affect productivity, yield and the quality of the harvested product. A simple statistical model for reconstructing three-dimensional (3D) canopy structures for various cultivar–training system (C × T) pairs has been implemented with special attention paid to balance the time required for model parameterization and accuracy of the representations from organ to stand scales. Such an approach particularly aims at overcoming the weak integration of interplant variability using the usual direct 3D measurement methods.

Model

This model is original in combining a turbid-medium-like envelope enclosing the volume occupied by vine shoots with the use of discrete geometric polygons representing leaves randomly located within this volume to represent plant structure. Reconstruction rules were adapted to capture the main determinants of grapevine shoot architecture and their variability. Using a simplified set of parameters, it was possible to describe (1) the 3D path of the main shoot, (2) the volume occupied by the foliage around this path and (3) the orientation of individual leaf surfaces. Model parameterization (estimation of the probability distribution for each parameter) was carried out for eight contrasting C × T pairs.

Key Results and Conclusions

The parameter values obtained in each situation were consistent with our knowledge of grapevine architecture. Quantitative assessments for the generated virtual scenes were carried out at the canopy and plant scales. Light interception efficiency and local variations of light transmittance within and between experimental plots were correctly simulated for all canopies studied. The approach predicted these key ecophysiological variables significantly more accurately than the classical complete digitization method with a limited number of plants. In addition, this model accurately reproduced the characteristics of a wide range of individual digitized plants. Simulated leaf area density and the distribution of light interception among leaves were consistent with measurements. However, at the level of individual organs, the model tended to underestimate light interception.Key words: Canopy, architecture, hemispherical, picture, light interception, radiative, balance, stochastic, modelling, virtual, plants     

Predicting the Growth Interactions between Plants in Mixed Species Stands using a Simple Mechanistic Model

The Conductance model is a simple mechanistic model used topredict the growth of species in monoculture or mixtures fromparameter values derived from plants grown in isolation. Incontrast to many mechanistic models that require extensive parameterization,the Conductance model is able to capture the growth of a broadrange of species using a few simplified assumptions regardingplant growth and easily derived species-specific parameter values.We examine the assumptions within the Conductance model thattotal leaf area per plant is proportional to total plant weight,and that an isolated plant has a projected crown zone area thatis proportional to the 2/3 power of its weight. Power ratherthan linear relations were found between weight and leaf areafor Brassica oleracea, Daucus carota, Matricaria inodora, Solanumnigrum,Stellaria media , Trifolium repens and Veronica persica.For all seven species, the value of the power was less thanunity. All species also exhibited a power relation between crownzone area and weight, with the slope of this relation beingless than 2/3 for B. oleracea, D. carota and S. media. Althoughmorphology type accounted for some of the variation in the parametervalues relating to light interception, there were considerabledifferences between species within upright or prostrate foliagespecies groups. The Conductance model was used to predict yieldsof B. oleracea, S. nigrum and V. persica grown in both monocultureand binary weed-crop mixtures over a range of temporal and spatialscales. After calibrating the model to non-competing plants,the model was used to predict growth of the weed and crop speciesin contrasting densities and stand types. In some crop-weedcombinations, predicted crop and weed weights were within 17%of observed values, with no systematic deviations. In others,systematic and large deviations occurred.Copyright 2001 Annalsof Botany Company Brassica oleracea L., Daucus carota L., Matricaria inodora L., Solanum nigrum L.,Stellaria media L., Trifolium repens L., Veronica persica L., competition, growth, leaf area, crown zone area, light, shoot morphology, canopy architecture     

Assessing the Geometric Structure of a White Clover (Trifolium repens L.) Canopy using3-D Digitising

A method was developed for assessing the three dimensional (3-D)geometric structure of white clover canopies. 3-D co-ordinatesof pre-defined points on leaves, petioles and stolons were measuredusing a Polhemus Fastrak electromagnetic 3-D digitiser. Digitisingprogressed downwards from the top of the canopy and plant partswere removed after they have been digitised. Leaflets were treatedas four quarter-ellipses, and petiole and stolons were treatedas cylinders. Leaf dimensions and areas calculated from 3-Dco-ordinates were within about 5% and 20% of direct measurementsmade with a ruler and a planimeter, respectively. Special softwareand freeware POV-Ray were used to reconstruct a virtual canopyfrom digitiser records and to calculate canopy characteristicssuch as leaf area index (LAI), petiole intersection area, andprofiles of leaflet areas and inclinations with height. It tookbetween 3 and 7 h to digitise 10 x 10 cm stands of clover andthe resulting information was considerably more comprehensiveand accurate than could have been obtained by the alternative‘point quadrat’ or ‘stratified clipping’methods.Copyright 2000 Annals of Botany Company White clover, Trifolium repens, geometric structure, leaf area, leaf angle, 3-D digitising     

Growth of Lettuce, Onion, and Red Beet. 1. Growth Analysis, Light Interception, and Radiation Use Efficiency

A field experiment was carried out to analyse the growth oflettuce, onion and red beet in terms of: (a) canopy architecture,radiation interception and absorption; (b) efficiency of conversionof absorbed radiation into biomass; and (c) dry matter partitioning.Growth analysis, total solar radiation interception, PAR interceptionand absorption by the crop canopy, ground cover, maintenancerespiration of onion bulbs and red beet storage roots were measured.Models for different leaf angle distribution and ground coverwere used to simulate light transmission by the crop canopy. The three crops are shown to have contrasting growth patternsfrom both a morphological and a physiological point of view.Lettuce showed very high light interception and growth afterthe early growth stages but, throughout the growth cycle, thisleafy crop showed the lowest radiation use efficiency due tothe respirational cost of the high leaf area. Onion showed alower early relative growth rate than lettuce and red beet.This was due partly to the low light interception per unit leafarea in the later stages of growth and partly to the low initialradiation use efficiency compared with the other two crops.On the other hand, thanks to more uniform distribution of theradiation inside the canopy, to the earlier termination of leafdevelopment and to the very low level of bulb respiration, onionshowed high radiation use efficiency and was able to producea large amount of dry matter. Red beet leaf posture and canopystructure resulted in high light interception and absorption.Its radiation use efficiency was lower than that of onion, partlyperhaps because of the more adverse distribution of the interceptedradiation fluxes within the canopy and partly because of thehigh respiration cost of a continuous dry-matter allocationto the leaves. However, this crop can accumulate a very largeamount of dry matter as leaf blade development and storage rootgrowth can both continue almost indefinitely, providing continuouslyavailable sinks. Ground cover gave a good estimate of the PAR interception onlyat low values of light interception but, in general, it underestimatedPAR interception in all three crops. Ratios between attenuationcoefficients established by considering PAR or total solar radiationand LAI or ground cover were calculated. Lettuce,Lactuca sativa L. var.crispa ; onion,Allium cepa L.; red beet; Beta vulgaris L. var.conditiva ; growth analysis; light interception and absorption; canopy architecture; ground cover; radiation use efficiency; maintenance respiration rate; dry matter distribution     

Effects of Intercropping on Growth and Reproductive Capacity of Late-emerging Senecio vulgaris L., with Special Reference to Competition for Light

Due to increased emphasis on long-term management of weed populationsin cropping systems with a reduced reliance on herbicides, theproduction of seeds by weeds that emerge after the criticalperiod for weed control is increasingly important. It was hypothesizedthat increased soil cover and light interception by a crop canopywould shorten the critical period for weed control and reducegrowth and fecundity of late-emerging weeds. This hypothesiswas tested in a series of field and glasshouse experiments inwhich competition for light was manipulated. Senecio vulgaris,an important weed in vegetable production systems, was chosenas the target plant, and canopies of pure and mixed stands ofleek and celery were used to provide shade. The time courseof light interception differed among the crop canopies. Increasingcompetition for light caused morphological changes to S. vulgaris,including a vertical shift in leaf area distribution. Increasedshading reduced biomass, capitula:shoot ratio and seed productionof S. vulgaris. However, the viability of seeds produced bythe shaded weed plants was not affected. Results indicate thatintercropping can increase light interception in a weakly competitivecrop such as leek and can contribute to weed suppression ina long-term strategy for weed management. Copyright 2001 Annalsof Botany Company Competition for light, late-emerging weeds, critical period, Apium graveolens L., celery, Allium porrum L., leek, Senecio vulgaris L., common groundsel, seed production, weed management, intercropping     

Evaluating a three dimensional model of diffuse photosynthetically active radiation in maize canopies

Diffuse photosynthetically active radiation (DPAR) is important during overcast days and for plant parts shaded from the direct beam radiation. Simulation of DPAR interception by individual plant parts of a canopy, separately from direct beam photosynthetically active radiation (PAR), may give important insights into plant ecology. This paper presents a model to simulate the interception of DPAR in plant canopies. A sub-model of a virtual maize canopy was reconstructed. Plant surfaces were represented as small triangular facets positioned according to three-dimensionally (3D) digitized data collected in the field. Then a second sub-model to simulate the 3D DPAR distribution in the canopy was developed by dividing the sky hemisphere into a grid of fine cells that allowed for the anisotropic distribution of DPAR over the sky hemisphere. This model, DSHP (Dividing Sky Hemisphere with Projecting), simulates which DSH (Divided Sky Hemisphere) cells are directly visible from a facet in the virtual canopy, i.e. not obscured by other facets. The DPAR reaching the center of a facet was calculated by summing the amounts of DPAR present in every DSH cell. The distribution of DPAR in a canopy was obtained from the calculated DPARs intercepted by all facets in the canopy. This DSHP model was validated against DPAR measurements made in an actual maize (Zea mays L.) canopy over selected days during the early filling stage. The simulated and measured DPAR at different canopy depths showed a good agreement with a R ² equaling 0.78 (n=120).     

Exploring the spatial distribution of light interception and photosynthesis of canopies by means of a functional-structural plant model

Background and Aims

At present most process-based models and the majority of three-dimensional models include simplifications of plant architecture that can compromise the accuracy of light interception simulations and, accordingly, canopy photosynthesis. The aim of this paper is to analyse canopy heterogeneity of an explicitly described tomato canopy in relation to temporal dynamics of horizontal and vertical light distribution and photosynthesis under direct- and diffuse-light conditions.

Methods

Detailed measurements of canopy architecture, light interception and leaf photosynthesis were carried out on a tomato crop. These data were used for the development and calibration of a functional–structural tomato model. The model consisted of an architectural static virtual plant coupled with a nested radiosity model for light calculations and a leaf photosynthesis module. Different scenarios of horizontal and vertical distribution of light interception, incident light and photosynthesis were investigated under diffuse and direct light conditions.

Key Results

Simulated light interception showed a good correspondence to the measured values. Explicitly described leaf angles resulted in higher light interception in the middle of the plant canopy compared with fixed and ellipsoidal leaf-angle distribution models, although the total light interception remained the same. The fraction of light intercepted at a north–south orientation of rows differed from east–west orientation by 10 % on winter and 23 % on summer days. The horizontal distribution of photosynthesis differed significantly between the top, middle and lower canopy layer. Taking into account the vertical variation of leaf photosynthetic parameters in the canopy, led to approx. 8 % increase on simulated canopy photosynthesis.

Conclusions

Leaf angles of heterogeneous canopies should be explicitly described as they have a big impact both on light distribution and photosynthesis. Especially, the vertical variation of photosynthesis in canopy is such that the experimental approach of photosynthesis measurements for model parameterization should be revised.     

Canopy photosynthesis and its relationship to plant productivity in near-isogenic cotton lines differing in leaf morphology

A 2-year study was conducted to determine the relationships between plant canopy photosynthesis, canopy light interception, and plant productivity of cotton (Gossypium hirsutum L.) exhibiting differing leaf morphologies. The near-isogenic lines were from a single background (MD 65-11) and represented the leaf shapes Normal (small leaf lobing), Sub-Okra (intermediate leaf lobing), Okra (large leaf lobing), and Super Okra (severe leaf lobing). The F₁ of a cross Normal × Okra (intermediate leaf lobing) and the F₂ (segregating 1:2:1 for Normal Sub-Okra, and Okra, respectively) were also grown. Reduced plant canopies were produced by Okra and Super Okra lines, which translated into increased light penetration to the ground, and hence, in reduced canopy photosynthesis. Integrated canopy photosynthesis (ICAP) was significantly associated with light interception by the plant canopy. Part of the remaining variability in ICAP was associated with confounding factors associated with plant maturity and other unmeasured genotypic factors. Intermediate (F₁ and Sub-Okra) and normal leaf types displayed the largest ICAP values in both years. Lint production was positively related to ICAP (R² = 0.53). The combination of high ICAP values and competitive lint yields indicate that intermediate lobed leaf morphologies offer promise as productive sources of physiological variation for cotton germplasm development.     

Do Variations in Local Leaf Irradiance Explain Changes to Leaf Nitrogen within Row Maize Canopies?

Numerous studies have dealt with the relationship between leafnitrogen content and leaf irradiance. However, most of themrefer to dense stands presenting reduced horizontal heterogeneityof foliage distribution. Both gradients of leaf nitrogen andleaf irradiance related to canopy depth are significant undersuch conditions, and modelling radiative exchange using a turbid-mediumanalogy and dividing the canopy into vegetation layers is sufficient.Conversely, row crops such as maize are characterized by stronghorizontal heterogeneity of foliage distribution and the one-dimensional(1D) approach may be unsuitable. We thus modelled the three-dimensional(3D) geometry of maize canopies with varying densities and atdifferent developmental stages using plant digitizing underfield conditions. The nitrogen content per unit area of eachleaf part was obtained subsequently by nitrogen analysis. Wenext calculated radiative exchange using a 3D volume-based approachwithin the canopies in order to estimate local leaf irradianceon a daily integration scale. Vertical gradients in leaf nitrogencontent per unit area observed in dense stands during the vegetativephase corresponded largely to those reported in the literature.We also identified significant gradients in nitrogen contentalong the leaves, which had not before been clearly demonstrated.Our study shows that local light climate during plant developmentplays a major role in leaf nitrogen distribution and remobilization.Moreover, brutal plant thinning involves rapid changes in leafnitrogen partitioning. It is concluded that taking account ofthe 3D heterogeneity of nitrogen and irradiance distributionmay have implications for modelling crop photosynthesis andproduction. Copyright 1999 Annals of Botany Company 3D plant architecture, horizontal gradients in leaf nitrogen, leaf irradiance, leaf nitrogen content per unit area, maize, nitrogen partitioning, nitrogen remobilization, virtual plant, Zea mays L.     

Light interception in apple trees influenced by canopy architecture manipulation

Improvement of light penetration within tree canopies has been a constant objective of fruit tree architecture manipulation through the setting up of training systems. Recently, centrifugal training, i.e. the removal of fruiting shoots in the tree centre and on the underside of branches, has been proposed to improve fruit size and colour as well as return-bloom as compared to conventional solaxe-trained trees with equivalent crop loads. The present study was conducted to quantify the benefits of centrifugal training on light interception by the fruiting shoots via computer-assisted three-dimensional representations of foliage geometry. Data were collected on six 5-year-old apple trees cv.Galaxy, trained either with solaxe or centrifugal training systems, using an electromagnetic 3D digitiser. The 3D distribution of the foliage in the tree canopy was recreated by combining both the spatial locations of shoots (as measured from 3D digitising) and foliage reconstruction. Light interception efficiency properties of the trees were characterised by silhouette to total area ratio (STAR) values computed from images of the 3D mock-ups. Compared to the solaxe system, centrifugal training significantly improved the STAR of the whole tree by 20%. It also increased both leaf area and STAR of the fruiting shoots by approximately 15%, regardless of their position in the canopy. In this paper, we discuss the role of this enhanced light interception by the canopy in increasing the autonomy of the fruiting shoot, i.e. improved fruit size and colour, and return-bloom.     

Radiation Interception, Partitioning and Use in Grass -Clover Mixtures

Mixed swards of perennial ryegrass /white clover were grownin competition under controlled environmental conditions, attwo temperatures and with different inorganic nitrogen supplies.The swards were studied after canopy closure, from 800 to 1200°C d cumulative temperatures. Clover contents did not varysignificantly during the period. A simulation model of lightinterception was used to calculate light partitioning coefficientsand radiation use efficiencies for both components of the mixturein this controlled environment experiment. Additionally, thissame radiative transfer model was applied to the field datafrom Woledge (1988) (Annals of Applied Biology112: 175 –186)and from Woledge, Davidson and Dennis (1992) (Grass and ForageScience47: 230 –238). The measured and simulated valuesof light transmission, at different depths in the mixed canopy,were highly correlated (P<0.001) with more than 80% of thetotal variance explained. The daily average of photosyntheticallyactive radiation (PAR) interception in a natural environmentwas estimated from simulations, for the field and controlledenvironment data. Under these conditions, white clover capturedsignificantly more light per unit leaf area than perennial ryegrassat low, but not at high, nitrogen supply. In the controlled environment experiment, the radiation useefficiency of the legume was lower than that of its companiongrass. For both species, radiation use efficiency was negativelycorrelated with the mean irradiance of the leaf. The role ofa compensation between light interception and light use forstabilizing the botanical composition of dense grass –cloverswards is discussed. Light interception; radiation transfer model; growth analysis; radiation use efficiency; white clover; perennial ryegrass; Trifolium repensL.; Lolium perenneL.; grassland     

What is the most prominent factor limiting photosynthesis in different layers of a greenhouse cucumber canopy?

Background and Aims

Maximizing photosynthesis at the canopy level is important for enhancing crop yield, and this requires insights into the limiting factors of photosynthesis. Using greenhouse cucumber (Cucumis sativus) as an example, this study provides a novel approach to quantify different components of photosynthetic limitations at the leaf level and to upscale these limitations to different canopy layers and the whole plant.

Methods

A static virtual three-dimensional canopy structure was constructed using digitized plant data in GroIMP. Light interception of the leaves was simulated by a ray-tracer and used to compute leaf photosynthesis. Different components of photosynthetic limitations, namely stomatal (S_L), mesophyll (M_L), biochemical (B_L) and light (L_L) limitations, were calculated by a quantitative limitation analysis of photosynthesis under different light regimes.

Key Results

In the virtual cucumber canopy, B_L and L_L were the most prominent factors limiting whole-plant photosynthesis. Diffusional limitations (S_L + M_L) contributed <15 % to total limitation. Photosynthesis in the lower canopy was more limited by the biochemical capacity, and the upper canopy was more sensitive to light than other canopy parts. Although leaves in the upper canopy received more light, their photosynthesis was more light restricted than in the leaves of the lower canopy, especially when the light condition above the canopy was poor. An increase in whole-plant photosynthesis under diffuse light did not result from an improvement of light use efficiency but from an increase in light interception. Diffuse light increased the photosynthesis of leaves that were directly shaded by other leaves in the canopy by up to 55 %.

Conclusions

Based on the results, maintaining biochemical capacity of the middle–lower canopy and increasing the leaf area of the upper canopy would be promising strategies to improve canopy photosynthesis in a high-wire cucumber cropping system. Further analyses using the approach described in this study can be expected to provide insights into the influences of horticultural practices on canopy photosynthesis and the design of optimal crop canopies.     

Saturation Deficit, Canopy Formation and Function in Sorghum bicolor (L.)

Hamdi, Q. A., Harris, D. and Clark, J. A. 1987. Saturation deficit,canopy formation and function in Sorghum bicolor (L.).—J.exp. Bot. 38: 1272–1283. Stands of two sorghum genotypes, SPV 354 and MK. 35-1, weregrown in controlled-environment glasshouses at three levelsof saturation vapour pressure deficit (SD), at the same temperatureand with unrestricted soil moisture. Vegetative growth was monitoredby growth analysis and non-destructive measurements were madeof leaf appearance, leaf extension and final size, and fractionallight interception. Rates of leaf appearance were reduced athigh SD in both genotypes, although this may have been an artefactof the method of measurement, and MK 35-1 produced leaves moreslowly than SPV 354. Leaf extension was also slowed as SD increasedand, since the duration of extension for individual leaves ofa given age remained constant, resulted in smaller leaf areaindices (L) in dry air than in humid air. The cumulative interceptionof radiation and the dry matter/radiation quotient (e) bothdecreased as SD increased. Key words: Sorghum, saturation deficit, canopy formation     

Changes in the vertical distribution of leaf area enhanced light interception efficiency in maize over generations of selection

Breeders select for yield, thereby indirectly selecting for traits that contribute to it. We tested if breeding has affected a range of traits involved in plant architecture and light interception, via the analysis of a panel of 60 maize hybrids released from 1950 to 2015. This was based on novel traits calculated from reconstructions derived from a phenotyping platform. The contribution of these traits to light interception was assessed in virtual field canopies composed of 3D plant reconstructions, with a model tested in a real field. Two categories of traits had different contributions to genetic progress. (a) The vertical distribution of leaf area had a high heritability and showed a marked trend over generations of selection. Leaf area tended to be located at lower positions in the canopy, thereby improving light penetration and distribution in the canopy. This potentially increased the carbon availability to ears, via the amount of light absorbed by the intermediate canopy layer. (b) Neither the horizontal distribution of leaves in the relation to plant rows nor the response of light interception to plant density showed appreciable trends with generations. Hence, among many architectural traits, the vertical distribution of leaf area was the main indirect target of selection.     

棉花冠层高光谱参数与叶片氮含量的定量关系

建立棉花(Gossypium hirsutum)氮素状况的光谱监测技术对于棉花营养诊断和长势估测具有重要意义。该研究利用冠层高光谱反射率及演变的多种高光谱参数,分析了不同施氮水平下不同棉花品种叶片氮含量与冠层反射光谱的定量关系,建立了棉花叶片氮含量的敏感光谱参数及预测方程。结果显示,棉花叶片氮含量和冠层高光谱反射率随不同施氮水平呈显著变化。棉花叶片氮含量的敏感光谱波段为600~700 nm的可见光波段和750~900 nm的近红外波段,且叶片氮含量与比值植被指数RVI [average (760~850), 700]有密切的定量关系,4个品种的平均决定系数在0.70左右。进一步分析表明,可以用统一的回归方程来描述不同品种、不同生育时期和不同氮素水平下棉花叶片氮含量随反射光谱参数的变化模式,从而为棉花氮素营养的监测诊断与精确施肥提供技术依据。     

A 3D Architectural and Process-based Model of Maize Development

A 3D architectural and process-based model of maize developmentwas implemented on the basis of the L-system software Graphtal,interfaced with physical models computing microclimate distributedon the 3D canopy structure. In a first step, we incorporatedin the software Graphtal additional functions that enable bi-directionalcommunication with external modules. A simple model for distributedphotosynthetically active radiation and the model for apex temperatureby Cellieret al. (Agricultural and Forest Meteorology63: 35–54,1993) were interfaced with Graphtal. In a second step we developeda L-system model for maize, where production rules for growthand development of organs are based on the current state ofknowledge of maize development as a function of temperature.Visual representation of the plant is based on the geometricalmodel of leaf shape by Prévot, Aries and Monestiez (Agronomie11:491–503, 1991). Finally, various data sets were used toevaluate the physiological aspects and the geometrical representation.It is concluded that environmental L-systems are a convenienttool to integrate biophysical processes from organ to canopylevel, and provide a framework to model growth of individualplants in relation to local conditions and ability to foragefor resources. However, progress is needed to improve both theknowledge of physiological processes at the organ level andthe calculation of physical environmental parameters; some directionsfor future research are proposed.Copyright 1998 Annals of BotanyCompany Growth model; 3D plant architecture;Zea maysL.; corn; temperature; L-system modelling; developmental physiology; virtual plant.     

Growth of Lettuce, Onion and Red Beet. 2. Growth Modelling

Data from a field experiment carried out on growth of lettuce,onion, and red beet were used: (a) to fit logistic, Gompertz,expolinear and ‘Scaife and Jones’ (Journal of AgriculturalScience, Cambridge86 : 83–91, 1976) functions using time,day-degrees and effective day-degrees; and (b) to test a mechanistically-basedmodel that combines the effects of potentially limiting variables,such as temperature and light, and allows for plant zone areain light interception (Aikman and Benjamin,Annals of Botany73 : 185–194, 1994). The use of day-degrees and effective day-degrees instead oftime, in general, improved the fit and gave a better estimateof growth parameters. The best fit was obtained by the Gompertzfunction for lettuce, and by the expolinear function for redbeet and for onion. The expolinear function seemed the mostreliable function in estimating the early relative growth ratewhich is the crucial value in all the mechanistic models. Thezone area model showed very good simulations for lettuce andred beet, but it requires a modification for canopy senescencein onion. Lettuce; Lactuca sativa L. var.crispa ; onion; Allium cepa L.; red beet; Beta vulgaris L. var.conditiva ; growth modelling; logistic; expolinear; Gompertz; zone area; time; day-degrees; effective day-degrees     

A Model for Plant and Crop Growth, Allowing for Competition for Light by the use of Potential and Restricted Projected Crown Zone Areas

Relations for competition for light are developed and used ina plant growth model applicable to the isolated plant, to plantsin even-aged monoculture and to plants in mixed-aged monoculture.In an isolated plant, it is assumed that a leaf area, proportionalto the plant mass, is contained within a crown whose projectedzone area is proportional to plant mass to the 2/3 power. Self-shadingprogressively reduces the specific growth rate. If light werethe sole limiting resource and were constant, one can derivea growth equation, dw/dt = rw[1 - exp (-KW^1/3)]KW^1/3, which,integrated, gives w^1/3 = K^-1 ln {1 + [exp (KW^1/3₀)-1] exp (rt/3)}.It approximates, initially, to a particular case of the Richards(1959) empirical growth equation. In even-aged evenly-spaced monocrops competing only for light,it is assumed that the zone areas merge at canopy closure, andgrowth then follows the expolinear equation of Goudriaan andMonteith (1990), giving a continuous function based on groundcover. For mixed-aged monocrops, we assume a phase of canopyclosure that affects the younger plants earlier than the olderones. Under varying environmental conditions in the field, plant growthmay be affected by other factors in addition, e.g. temperature.In the growth conductance model of Aikman and Scaife (1993),the shading expressions are applied to the light-dependence. Data from two sowings of cabbage and carrot in even-aged andmixed-aged monocrops were used to test the model. The parametervalues derived from the even-aged monocultures predict the growthrates in the mixed-aged monocultures better than models whichassume uniform canopies.Copyright 1994, 1999 Academic Press Growth, model, monocrop, even-aged, mixed-aged, PAR, density, competition, light, shading, zone area, ground cover, temperature, carbon dioxide, expolinear, carrot, Daucus carota L., cabbage, Brassica oleracea L     

Photosynthesis of Stands of Tomato, Cucumber and Sweet Pepper Measured in Greenhouses under Various CO2-concentrations

The rate of net photosynthesis (P) of whole plant stands oftomato (Lycopersicon esculentum Mill.), cucumber (Cucumis sativusL.) and sweet pepper (Capsicum annuum L.) was measured in sixlong-term experiments in large greenhouses under normal operatingconditions and CO₂-concentrations between 200 and 1200 µmolmol^-1. The objective was to quantify the responses to lightand carbon dioxide and to obtain data sets for testing simulationmodels. The method of measuring canopy photosynthesis involvedan accurate estimation of the greenhouse CO₂ balance, usingnitrous oxide (N₂O) as tracer gas to determine, on-line, theexchange rate between greenhouse and outside air. The estimatedrelative error in the observed P was about ± 10%, exceptthat higher relative errors could occur under particular conditions. A regression equation relating P to the photosynthetically activeradiation, the CO₂ concentration and the leaf area index explained83-91% of the variance. The main canopy photosynthesis characteristicscalculated with the fitted regression equations were: canopyP_max 5-9 g m^-2 h^-1 CO₂ uptake; ratio P_max/LAI 1·5-3 gm^-2 h^-1; light compensation point 32-86 µmol s^-1 m^-2;light use efficiency (quantum yield) at low light 0·06-0·10µmol µmol^-1 and CO₂ compensation point 18-54 µmolmol^-1. The results were related to the prevailing conditions.Copyright1994, 1999 Academic Press Canopy photosynthesis, Capsicum annuum L., carbon dioxide, CO₂, CO₂ balance, CO₂ use efficiency, cucumber, _{Cucumis sativus} L., glasshouse, greenhouse, light use efficiency, Lycopersicon esculentum Mill., sweet pepper, tomato, tracer gas     

Carbon Balance of Tall Fescue (Festuca arundinacea Schreb.): Effects of Nitrogen Fertilization and the Growing Season

The C balance of a tall fescue sward grown under different ratesof N fertilization in summer, autumn, and spring was calculatedusing models derived from measurements of shoot growth, canopygross photosynthesis, shoot respiration and of C partitioningto the roots. Under the diverse growing conditions associatedwith the seasons and the N fertilization, C utilization forabove- and below-ground biomass accumulation never exceeded39 and 14% of the canopy gross photosynthesis, respectively.Carbon losses attributed to root respiration and exudation,which were estimated by difference between canopy net photosynthesisand total growth, ranged between 3 and 30% of canopy gross photosynthesis.Seasonal differences in shoot growth could be attributed tothe amount of intercepted radiation, the radiation-use efficiencyand the C partitioning to the roots. The effect of N deficiencyon shoot growth can be attributed to its effects on canopy photosynthesis(principally resulting from changes in intercepted photosyntheticallyactive radiation) and C partitioning. In comparison with theeffect on shoot growth, the effect of the N deficiency on thecanopy gross photosynthesis per unit of light intercepted overthe regrowth cycle was limited. It is concluded that most ofthe effect of N fertilization on shoot growth is due to changesin C partitioning which result in faster leaf area developmentand greater light interception.Copyright 1994, 1999 AcademicPress Tall rescue, Festuca arundinacea Schreb., carbon balance, nitrogen, grass, fertilization